A pre-press workflow system, as disclosed e.g. in patent application WO 01/25907, may include several processes. One of these processes is imposition. As discussed in patent U.S. Pat. No. 6,046,818, imposition is the pre-press process of arranging the pages, that will be printed on the same sheet, in such a way that a proper sequence or position of each page relative to the other pages on the sheet is achieved. Arranging the pages is required because, when e.g. a book or a leaflet is manufactured, several pages of the book or leaflet are printed by the printing press on the same sheet. After printing, the sheet is folded and possibly cut and bound together with other processed sheets. In the resulting book or leaflet, the pages of course have to follow one another in the correct order; this is a job of the imposition process. Thus, the pre-press process of imposition is performed in view of post-press processes such as fold and cut operations.
An imposition plan represents the layout according to which the individual pages are arranged on a sheet, possibly including the relevant dimensions, i.e. the dimensions of the sheet, the dimensions of the individual pages and the dimensions of the spaces at the borders and between the individual pages on the sheet. To determine an imposition plan, several data have to be taken into account, such as the size of the sheet, the size of the individual pages, the possibilities of the press and of the folding machine that will be used.
It is customary to use a set of predefined imposition plans, often called imposition templates, to determine an imposition plan. Such a predefined imposition plan or imposition template gives the layout of the individual pages on the sheet without the dimensions. To select a suitable imposition template for a given print job, a user may be assisted by a computer program that shows a set of imposition templates. The user then selects an imposition template from this set and adds the relevant dimensions to the selected imposition template; usually the user is also assisted in this step by the computer program. The selection of the imposition template is based on the user's experience, on naming conventions (the names of the imposition templates may reflect the number of pages on a sheet and the binding method, e.g. “8-up saddle stitched”) and very often on habit—most companies only use a very limited number of imposition templates. A company may use e.g. only four imposition templates that cover the majority of print jobs of the company; out of these four imposition templates, the user then selects the imposition template that will be used for a given job, based on his professional knowledge, i.e. his experience.
However, the imposition plan that was determined in this way is not necessarily optimal. If a sheet is used onto which 3×4 DIN A4 pages can be printed, for a page size somewhat smaller than DIN A4 the optimal imposition is not necessarily 3×4 (“3×4” means that three pages are arranged next to each other in, e.g., the width direction of the sheet, and four pages are next to each other in, e.g., the length direction of the sheet). Moreover, the imposition templates were set up for common cases and thus incorporate only some possibilities of common folding machines. Therefore, quite some possibilities of folding machines are not used at all.
There is thus a need for an improved method for determining an imposition plan.